Problem with newborn KRX3: Very poor sensitivity.

[Jon Kåre Hellan]

I have installed the subreceiver in my K3 and done some testing. It
seems to work, except that sensitivity is very poor. I've been listening
to one receiver in each headphone. On the sub-rx. the strongest signals
on the band just come up above the noise. The effect is much stronger
than swithing the attenuator in and out.

I've gone over all TMP cables carefully, and had the sub-rx in and out
of the K3 several times. Behaviour has been the same every time.

To compare sub and main signals, I linked the two VFOs. Both RF gains
were at max. Signals which were clear with the main AF gain at 7 - 8
o'clock became audible just above the nose at 3 o'clock AF gain on the sub.

To check that I was actually hearing the sub-rx, and not some kind of
crosstalk from the main, I unlinked the VFOs and verified that what I
heard in the sub-rx tuned with the main. I also checked that it
responded to sub-rx width and offset tuning, and not to main.

With a strong signal, I moved the same antenna between main and aux
input and found that signals from both sounded about the same on the sub-rx.

I've varied bandwidth from min to max. It switches between filters as
expected, and there are no sudden changes in signal level.

To me it sound like the problem must be either on the KRX3 board or on
the way out from there. 2 independent signal inputs give the same
result, so they're either both OK or both bad in exactly the same way.
If there was anything wrong with the cable from the synthesizer board or
the one from the frequency reference, I wouldn't expect the sub-rx to
work at all. Does this make sense?

Suggestions, anyone?

73
Jon LA4RT

Jon Kåre Hellan, Trondheim, Norway

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[Jon Kåre Hellan]

Jon Kåre Hellan wrote:
> I have installed the subreceiver in my K3 and done some testing. It
> seems to work, except that sensitivity is very poor. I've been listening
> to one receiver in each headphone. On the sub-rx. the strongest signals
> on the band just come up above the noise. The effect is much stronger
> than swithing the attenuator in and out.

With excellent help from Elecraft support, I was able to pinpoint where
the signal was lost. Turns out an RF choke had fallen off the KRX3
board. As luck would have it, I hadn't thrown out the bags yet, and the
choke was still in the bag. The KRX3 works now.

I suspect Elecraft will want a word with the contractor who supplies the
boards :-)

But I'm feeling somewhat like an owner of a British car in the 70's.
Next time I'll look for loose parts in the bags *before* putting things
together.

73
Jon LA4RT
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